1. Field of the Invention
The present invention relates to an instrument with crossed-coil type movable magnet generally used in speedometers, tachometers and other instruments for motor vehicles.
2. Description of Prior Art
An instrument with a crossed-coil type movable magnet is generally composed of an indicator section, a drive section and a converter section. The indicator section forms a body of this instrument. In this instrument a pointer shaft is projectingly installed; a movable magnet rotating on the center of the pointer shaft is installed within a bobbin; and a crossed coil is disposed intersecting perpendicularly to the bobbin. The drive section, receiving a signal from the converter section, applies a specific current to the crossed coil. And the converter section functions to convert an input from an object under measurement into an electrical signal which is easy to process in the drive section. Therefore, the specific currect is applied to the crossed coil in accordance with the amount of input from the object under measurement to develop a magnetic field in the crossed coil, which in turn rotates the movable magnet in the direction of composite magnetic field of the magnetic field. The pointer also turns with it, indicating a measured amount.
If it is possible to change the direction of energizing the crossed coil, a composite magnetic field can be established in any direction through 360 degrees. Generally, the current corresponding to a sine value of a designed pointer angle is applied to one crossed coil and the current corresponding to the cosine value to the other coil; the drive section receives the input from the aforesaid converter, outputting a corresponding value described above. (Refer to U.S. Pat. No. 3,636,447.) There is provided the converter section so that, in this case, the drive section can easily perform processing to output the aforesaid corresponding value. In general, the frequency input is converted into a voltage output and inputted into the drive section. (Refer to Laid-Open Japanese Patent Application No. Sho 61-120063.)
When the processing means in the drive section of the aforesaid instrument with crossed-coil type movable magnet is operated by a digital signal, the input from the object under measurement is converted into a specific digital signal at the converter, being supplied to the drive section, which in turn outputs correspondingly to this digital signal. The indication resolution of the instrument, therefore, is determined correspondingly to the fragmentation of digital signal (driving input) described above. The higher the resolution of pointer indication of the instrument, the smoother the pointer operates, thus resulting in improved instrument performance. Therefore, sending to the drive section a digital signal that has been further fragmented at the aforementioned converter can provide an instrument of such higher pointer indication resolution.
The fragmentation of the converter output, however, increases the processing mechanism of the drive section corresponding thereto.